1. The Field of the Invention
The present invention relates to a branch candidate selecting method in a mobile station in the case where the mobile station detects a plurality of addition branch candidates and deletion branch candidates, and to a diversity handover branch control method on a network side in executing diversity handover.
2. The Relevant Technology
Recently, code division multiple access (CDMA) technology has been proposed as one of promising radio transmission methods for implementing multimedia communications in the next generation mobile communication network systems. A CDMA system carries out diversity handover (DHO) that establishes multiple communication links (branches) between a mobile station and a plurality of base stations while the mobile station is moving near a boundary of a radio area, and communicates by performing signal combining (selection combining) on the multiple communication links. In the diversity condition, it is possible to increase a radio capacity by controlling such that the mobile station and the base stations can communicate at minimum transmission power (transmission power control). Furthermore, it is possible in the diversity condition to eliminate instantaneous chopping during handover, which can occur in the conventional time division multiple access (TDMA).
Establishing a new branch in the DHO is specifically referred to as xe2x80x9caddition DHOxe2x80x9d in the DHO, and deleting a communication branch not contributing to the communications in the diversity condition is specifically referred to as xe2x80x9cdeletion DHOxe2x80x9d in the DHO. To carry out the addition DHO and deletion DHO, the mobile station normally detects a candidate of the addition DHO (called xe2x80x9caddition DHO candidatexe2x80x9d or xe2x80x9caddition branch candidatexe2x80x9d), and a candidate of the deletion DHO (called xe2x80x9cdeletion DHO candidatexe2x80x9d or xe2x80x9cdeletion branch candidatexe2x80x9d). Detecting an addition or deletion branch candidate by monitoring a radio condition (transmission loss, for example) of a perch in the current sector or peripheral sectors, the mobile station notifies the network side of the detected candidate. The network side performs the DHO (addition DHO or deletion DHO) based on the notified candidate. The term xe2x80x9cnetwork sidexe2x80x9d usually refers to a switching center or a control center of base stations, it is possible to provide this function to the base stations.
The mobile station communicates with the base stations using individual radio links (radio branches) associated with the base stations. A switching center comprises cable links (cable branches) connecting it with the base stations that are communicating with the mobile station, and carries out, with a handover (HO) processor or a diversity handover trunk (DHT), the selection combining of the signals sent from the base stations. The fundamental operation of the diversity handover branch is disclosed in Japanese Patent Application Laid-open No. 9-508773 (1997), and network configurations and control methods of the diversity handover trunks are disclosed in Japanese Patent Application No. 8-348900 (1996).
Because of hardware implementation or the like, there are provided an upper limit to the number of radio branches (a maximum radio branch number) that the mobile station can establish simultaneously, and an upper limit to the number of cable branches (a maximum cable branch number) that the DHT in the switching center can connect or process simultaneously. The upper limit to the number of communication branches (the maximum communication branch number) that can be established in the diversity condition equals the smaller one of the maximum numbers of the radio branches and cable branches. In ordinary systems, it is designed that the maximum radio branch number becomes equal to the maximum communication branch number to make effective use of radio resources by giving priority to them.
However, conventional papers (for example, Shimizu, et al. xe2x80x9cHandover equipment and control method in next generation mobile communication systemsxe2x80x9d, General assembly of the Institute of Electronics, Information and Communication Engineers of Japan, 1997) handle the subject only under the assumption that the control of branches to be added or deleted is limited to a single branch, and do not handle simultaneous control of a plurality of addition branches and deletion branches. It is not specified in ITU-T recommendation Q.FIF version 6, as well.
As mentioned above, since the control of the branches to be added and deleted is carried out on one by one basis in the prior art, N times of control is required in principle to control N branches. However, the mobile station can detect a plurality of deletion branch candidates and addition branch candidates at the same time, because their detection depends on the ambient radio condition.
In such a case, a number of times of similar control operations are repeated between the mobile station and the switching center, which is not only inefficient, but also takes an extra time for the control until the entire handover control is completed.
Taking account of the addition DHO of a single branch, the prior art sets the maximum cable branch number at the maximum radio branch number plus one. Thus, the network side can prepare the branches in cable sections by the number greater than the maximum radio branch number by one. This enables a simple switching operation in the radio sections to complete the addition DHO by adding one cable branch from among the prepared cable branches without deleting the communication branch even in the case where one branch is added to the maximum number of branches.
However, such a method that follows the prior art, in which the maximum cable branch number is set at the number greater than the maximum radio branch number by one, has a problem of impairing effective control because of the network side control repeated by the number of addition branch candidates. Furthermore, no prior art takes account of handling any addition branch candidates that have not been prepared in the cable section, even though they have higher DHO priority than the communication branches, because the control unit is for a single branch and the maximum cable branch number is limited.
Therefore, the present invention is implemented to solve the foregoing problems. An object of the present invention is to provide a branch candidate selecting method in a mobile station and a control method of diversity handover branches on a network side, considering a maximum cable branch number and a maximum radio branch number of the mobile station in the case where the mobile station detects a plurality of addition branch candidates and deletion branch candidates. In the first aspect of the present invention, there is provided a mobile communication system comprising a mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein the mobile station notifies the switching center of information on one or more addition branch candidates between the mobile station and the base station, and of information indicative of precedence of the addition branch candidates; and the switching center performs handover control in accordance with the information notified.
Here, information transmitted from the mobile station to the switching center may further include information on one or more communicating branches between the mobile station and the base station.
The switching center may establish a communication branch between the mobile station and the switching center using information on one or more communicating branches between the mobile station and the base station, the transmitted information on one or more addition branch candidates between the mobile station and the base station, and the information on the precedence of the addition branch candidates.
The switching center may establish, when a sum total of a number of communicating branches and a number of the addition branch candidates exceeds a maximum radio branch number simultaneously establishable in communications between the mobile station and the base station, a communication branch in order of precedence up to a maximum cable branch number that can be processed simultaneously by the switching center.
In the second aspect of the present invention, there is provided a mobile station of a mobile communication system comprising the mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein information transmitted from the mobile station to the switching center includes information on one or more deletion branch candidates between the mobile station and the base station.
In the third aspect of the present invention, there is provided a mobile communication system including a mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein the switching center creates settings for deleting one or more communicating branches.
In the fourth aspect of the present invention, there is provided a mobile station of a mobile communication system including the mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein the mobile station notifies the switching center of information on one or more addition branch candidates between the mobile station and the base station, and of information indicative of precedence of the addition branch candidates.
Here, the mobile station may notify, while communicating with the base station using a maximum number of radio branches simultaneously establishable, the switching center of addition of the addition branch candidates, when precedence of an addition branch candidate to be added exceeds, by an amount of a predetermined threshold value, precedence of a communicating branch with lowest precedence.
Information transmitted from the mobile station to the switching center may further include information on one or more communicating branches between the mobile station and the base station.
In the fifth aspect of the present invention, there is provided a diversity handover branch control method in a mobile communication system including a mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein information transmitted from the mobile station to the switching center includes information on one or more deletion branch candidates between the mobile station and the base station.
In the sixth aspect of the present invention, there is provided a diversity handover branch control method, in which a mobile station detects one or more addition branch candidates constituting handover candidates in communications between the mobile station and a base station connected to the mobile station, and notifies a switching center connected to the base station of the addition branch candidates, wherein information transmitted from the mobile station to the switching center includes information on one or more addition branch candidates between the mobile station and the base station, and information indicative of precedence of the addition branch candidates.
Here, the information transmitted from the mobile station to the switching center may further include information on one or more communicating branches between the mobile station and the base station.
The information indicative of precedence may be an order of arrangement of information on the communicating branches and information on the addition branch candidates.
The information indicative of precedence may consist of numerals representing information on the communicating branches and information on the addition branch candidates.
The information indicative of precedence may be an order of arrangement of information on the addition branch candidates.
The order of arrangement may be a decreasing order of transmission losses.
The information indicative of precedence may consist of numerals representing information on the addition branch candidates.
The switching center may establish the communication branches between the mobile station and the switching center using information on one or more communicating branches between the mobile station and the base station, transmitted information on the one or more addition branch candidates, and information indicative of precedence of the addition branch candidates.
The switching center may establish, when a sum total of a number of communicating branches and a number of the addition branch candidates exceeds a maximum radio branch number simultaneously establishable in communications between the mobile station and the base station, a communication branch in order of precedence up to a maximum cable branch number that can be processed simultaneously by the switching center.
The maximum cable branch number may be greater than the maximum radio branch number by N, where N is an integer equal to or greater than one.
The mobile station may make a decision of the addition branch candidates again and notify the switching center of the addition branch candidates, when a total sum of a communicating branch number and an addition branch number exceeds the maximum cable branch number, and hence the addition branch candidates are not added because of restrictions on an upper limit of the maximum cable branch number.
The switching center may store, when the addition branch candidates are not added because of the upper limit of the maximum cable branch number, branch candidates that cannot be added because of the upper limit of the maximum cable branch number, and autonomously carries out control.
In the seventh aspect of the present invention, there is provided a mobile communication system including a mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein information transmitted from the mobile station to the switching center includes information on one or more deletion branch candidates between the mobile station and the base station.
In the eighth aspect of the present invention, there is provided a diversity handover branch control method in a mobile communication system comprising a mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein the switching center creates settings for deleting one or more communication branches.
In the ninth aspect of the present invention, there is provided a diversity handover branch control method in a mobile communication system including a mobile station, a base station connected to the mobile station, and a switching center connected to the base station, wherein the mobile station autonomously creates settings for deleting one or more communication branches.
In the tenth aspect of the present invention, there is provided a diversity handover branch control method, in which a mobile station detects one or more communication branches constituting handover candidates, and notifies a switching center of the communication branches, wherein the mobile station autonomously deletes one or more communication branches, and subsequently notifies the switching center of the deleted branches via a remaining communication branch.
In the eleventh aspect of the present invention, there is provided a diversity handover branch control method, in which a mobile station detects one or more communication branches constituting handover candidates, wherein the mobile station autonomously deletes one or more communication branches, and subsequently a switching center, which is connected with the mobile station through a base station, deletes a corresponding cable branches by detecting disconnection of the radio branch.
In the twelfth aspect of the present invention, there is provided a diversity handover branch control method, in which a mobile station detects one or more addition branch candidates constituting handover candidates in communications between the mobile station and a base station connected to the mobile station, and notifies a switching center connected to the base station of the addition branch candidates, wherein the mobile station does not notify, when a communicating branch number equals a simultaneously establishable maximum radio branch number between the mobile station and the base station, the switching center of information on addition branch candidates that are unlikely to be added in diversity handover.
In the thirteenth aspect of the present invention, there is provided a diversity handover branch control method, in which a mobile station detects one or more addition branch candidates constituting handover candidates in communications between the mobile station and a base station connected to the mobile station, and notifies a switching center connected to the base station of the addition branch candidates, wherein the mobile station notifies, when a sum total of a communicating branch number and an addition branch candidate number is equal to or less than a simultaneously establishable maximum radio branch number between the mobile station and the base station, the switching center of the addition branch candidates.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.